1. Field of the Invention
The present invention relates to a method for the production of hot-rolled wide strip in a production plant which includes a continuous casting plant for thin slabs having a thickness of between 40 and 70 mm, an equalizing furnace and a rolling mill, wherein the temperature of the thin slab when exiting the continuous casting plant is above 950.degree. C.
The present invention also relates to a production plant for carrying out the method.
2. Description of the Related Art
In a production plant for the economical production of hot-rolled wide strip which has become known under the name CSP-plant, a thin slab having a thickness of 40 to 70 mm is rolled in a multiple-stand rolling mill train directly after being produced in the continuous casting plant and after the temperature equalization. The temperature of the thin slab after leaving the continuous casting plant is usually between 950.degree. and 1100.degree. C. A temperature of, for example, 1100.degree. C. which is uniform over the slab thickness and slab length is adjusted in the roller hearth furnace.
The method carried out in the above-described plant is characterized by the fact that no austenite to ferrite/perlite conversion takes place before the first deformation in the rolling mill train. The primary austenite obtained after the solidification in the continuous casting plant remains unchanged up to the first deformation in the rolling mill train.
The described method ensures the highest possible savings in energy, particularly in those embodiments in which the temperature following the continuous casting plant is slightly below the desired temperature following the roller hearth furnace. In these cases, the energy required for the temperature equalization in the roller hearth furnace can be reduced to an absolute minimum.
This method has been found very useful for the use of first-choice scrap with admixtures of directly reduced iron as well as for the use of converter-treated crude steel. However, disadvantages are expected when the method is used with second-choice scrap, particularly with admixtures of copper. During the formation of scale as the steel travels through the roller hearth furnace, the released copper will collect at the grain boundaries of the primary austenite and loosen the interconnection of the grain boundaries in the surface area. Depending on the degree of the copper content and depending on the degree of scaling, this phenomenon may lead to the so-called solder breakage during the deformation in the subsequent rolling mill train.